It is known in the art to react a polyol and a dibasic carboxylic acid to produce an unsaturated polyester resin. When a simple polyol is utilized to limit the chain extension to only a few units, the products are referred to as oligomers. Diluents are used with these resins to reduce the viscosity of formulation to levels suitable for the required method of coating. These diluents are usually distinct from resins in that they are discrete molecular units. Thus, the diluents are often termed monomers.
A wide range of reactive oligomers have been used as components in radiation (via electron beam or ultraviolet) curable inks and coatings. The majority of these employ acrylic functionality to induce a rapid cure. However, resins with maleic or fumaric functionality have found uses in certain applications such as wood coatings and, to a limited extent, lithographic inks. These resins, while not as reactive as acrylic-functional resins, are less expensive. In appropriate applications, coating formulators will trade a certain amount of cure speed for lower costs.
These lower cost resins are unsaturated polyesters typically produced from a glycol and a dibasic carboxylic acid, most often maleic anhydride. Usually phthalic anhydride or isophthalic acid is added to the polyester to control functionality and to increase hardness. Yet, even with the aromatic acid, these resins remain low-melting solids or semi-solids incapable of being flaked into solid chips. It is recognized in the art that a resin must have a softening point of at least 80.degree. C. in order to be uniformly flaked.
This inability to be flaked requires that the resins be dissolved in monomers and sold as solutions. Monomers play the same rheological adjustment and pigment-wetting role in radiation-curable coatings as do solvents in conventional coatings. Thus, instead of the coatings formulator having one solid resin he can introduce into a number of systems, the formulator is currently required to specify the resin-containing monomer solution or solutions needed for each system.
Therefore, it is the object of this invention to produce a radiation-curable resin that is 100% solid at a temperature of 80.degree. C., and thus is capable of being flaked. The invention would result in a lowering of shipping, handling, and inventory costs for coating and ink producers.